An image of A common seal resting on a Dartmouth beach

DOI: https://doi.org/10.58248/HS42

Overview of change

UN Sustainable Development Goal 14 to “conserve and sustainably use the oceans, seas and marine resources for sustainable development” will require rebuilding marine ecosystems to provide the benefits derived from biodiversity. Research suggests examples of restored and protected habitats are growing, with marine protected areas (MPAs) increasing from 0.9% of the ocean in 2000 to 7.4% now.1 The Convention on Biological Diversity (CBD) proposal for 30% of the global ocean to become MPAs by 2030 would require agreement on marine biodiversity beyond areas of national jurisdiction under the UN Convention on the Law of the Sea, as 61% of the oceans are international waters.2,3,4 Research has identified global priorities for the expansion of marine conservation efforts by mapping more than 22,000 marine species and habitats, and modelling species ranges. This suggests the total ocean area required for conservation varies from 26–41%, which would need to be protected through effective strategies such as no-fishing zones and community marine reserves.5

Challenges and opportunities

Most MPAs do not limit fishing and its associated habitat damage,6 and compliance is often poor in those that do.7,8 MPAs are often sited in remote areas to minimise enforcement costs and conflicts (just 20 large sites in the remote open ocean account for the majority of the world’s MPAs) but would need to be in highly used coastal areas to make substantial conservation gains.9,10,11,12 If the 2.7% of the world’s ocean area that does effectively exclude fishing were to be increased by an additional 5%, modelling has suggested this could increase future catch by at least 20% via spillover to unprotected areas,13,14 as well as conserving biodiversity and securing marine carbon stocks.15 But increasing the extent of highly protected marine areas would be strongly opposed by the fishing industry.12,15 Rare species most sensitive to exploitation also respond strongly to protection, with biodiversity benefiting most from a network of protected areas in a region covering habitats for different species.16

Around 500 million people live along coastlines with coral reefs that are vulnerable to degradation.17 Natural infrastructure, such as conserved and restored coral reefs and mangrove forests, could reduce the impacts of climate change on communities in coastal areas, including storm surges and other sea level rise effects, as well as increasing biodiversity through habitat provision.18 For example, seagrass meadows are nurseries for fish populations, weaken storm surges and provide numerous other services to coastal communities, as well as sequestering carbon from marine, terrestrial and freshwater systems.19 An estimated 7% of seagrass habitat is being lost worldwide each year, and at least 22 of the world’s 72 seagrass species are in decline, because of pollution, coastal development, dredging and fishing, with only 26% falling within MPAs.20 The UK’s historical seagrass meadows may have stored 11.5 megatonnes (Mt) of carbon, but have been reduced to 8,493 ha storing only 0.9 Mt of carbon.21 Saltmarshes are also important coastal fringe ecosystems with high carbon sequestration rates that have undergone global decline.22,23,24

Only 2.5% of tropical reefs are formally protected and conserved through laws and regulations, but most are not strategically placed to benefit nearshore fish populations and the human communities that depend on them.25 Little is known about the context in which different reef management tools can help to achieve multiple social and ecological goals. Only 5% of 1,800 of reefs surveyed are able to provide a range of services, including healthy fish biodiversity.26 Research on coral restoration strategies has had some success,27,28,29 but it is unclear whether coral conservation can succeed without a rapid reduction in greenhouse gases to reduce the climate change impacts on corals.30,31

Key unknowns

Since the 1950s, the oceans have absorbed roughly 93% of the additional heat accumulation in the climate system, with global and regional changes in factors such as temperature and salinity.32 Recent widespread coral reef bleaching events driven by global heat waves suggest conventional conservation approaches will not be enough.33 Changes are occurring in the species that make up coral reefs and in their distribution; extending their range toward higher latitudes. This raises questions about whether previous states can be restored,34 and how to manage changing ecosystems.35 It is uncertain if novel interventions,36 such as thermal selection experiments to develop strains of coral symbionts that confer enhanced bleaching tolerance to corals,37 can help reefs adapt beyond 1.5°C warming. In addition to the climate change impacts of ocean heating and acidification,29 coral reefs may be degraded by declining oxygen levels caused by nutrient pollution.38,39

The areas of deep ocean that provide suitable conditions for species, in terms of suitability or ecological niche, will change faster than surface waters under all climate change scenarios. This suggests the need to reduce other pressures, such as fishing and deep-sea mining.40 Habitat suitability models can help assess the consequences of altered dispersal of species’ larvae (the early developmental stages of marine species such as shellfish),41 predict climate refugia, and identify vulnerable regions for multiple species under climate change,42,43 but the data about the long-term effects of deep-sea mining are limited.44

Ice core data suggest levels of phytoplankton productivity in the North Atlantic have declined since the 19th Century in response to climate change,45,as well as reductions in the populations of marine fauna;46,47 further declines will affect ecosystems and fisheries.

Key questions for Parliament

  • What are the implications of the 2021 CBD targets for protecting marine habitats and species?48 Should the UK be taking a leadership role in the UN’s Decade of Ocean Science given its strengths in marine science?49
  • Given the UK Marine Strategy and potential highly protected marine areas,50,6 will UK territorial waters and the MPA network implementation around UK Overseas Territories meet SDG 14 despite climate change effects?51,52
  • Will UN Convention on the Law of the Sea negotiations reach agreement on a network of high seas MPAs?53

Likelihood and impact

Successfully implementing post 2021 CBD objectives to restore marine biodiversity will require interventions that can address pressures on marine ecosystems.

Research for Parliament 2021

Experts have helped us identify 30 areas of change to help the UK Parliament prepare for the future.

References

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Photo by Pascal Mauerhofer on Unsplash

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